No need for tour.. they are pricey and you don't get enough time there to enjoy the grounds properly.
Easy to do on your own.. really.
With the Museum pass you do get free general admission,, if you go on a fountain show day ( which I would avoid like plague having accidently done it once ) then you simply pay at the entrance at the back of the palace.. don't worry.. its not a long line ...
To go to Versailles you simply that the RER there.. its about 45 minutes and its the last stop ( so you wont "miss it") you get off train with a hundred other people all going to same place,, lol,, you walk about 5-10 minutes ( and there are signs pointing to Chateau) .
Arrive BEFORE it opens.. yes.. you skip the line for tickets.. but not for the Security entrance and the lines for that can be long too. We made the mistake of arriving at 10.30 am one day and waited at least 45 minutes in roasting sun just to go through security .
Cost for fountain show was 8 euros last year.
The chateau is overwhelming and crowded.. but once you get out spend some time and really see the grounds and outbuildings.. and Marie Antionettes Hamlet. You can walk.. lots of walking.. or pay for a little shuttle bus to take you to ends of grounds.. ( I always walk so can't remember cost)
Be sure to go into the gardens behind the Grand Trianon.. pretty flower garden ( most of the gardens are the more formal bushes etc) and best of all.. the view up the canal to the palace.. its pretty special.